SAA-C03 Design Resilient Architectures Practice Question
A startup runs a stateless web tier on Amazon EC2 instances in an Auto Scaling group that spans three Availability Zones. The team wants the application to keep serving requests even if one instance becomes unresponsive, without operator involvement. What should the solutions architect configure?
⚠ Common exam trap
The trap here is expecting an Elastic IP or scheduled scaling to provide automatic failover for an unhealthy instance, when only health-checked load balancing removes it from service.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An Application Load Balancer with health checks that route traffic only to healthy targets.
Health-checked load balancing is the mechanism that detects an unresponsive instance and removes it from the traffic path automatically. Because the tier is stateless and already spans three Availability Zones, the Application Load Balancer can shift requests to remaining healthy instances while the Auto Scaling group replaces the failed one.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
An Application Load Balancer with health checks that route traffic only to healthy targets.
Why this is correct
The load balancer performs health checks against each target and stops sending traffic to targets that fail, so an unresponsive instance is removed from rotation automatically. Combined with the Auto Scaling group, replacement capacity is launched, keeping the stateless web tier available without human action.
- ✗
A Network Load Balancer configured with a single target group and no health checks.
Why it's wrong here
Without health checks the load balancer continues to forward connections to the unresponsive instance, producing failed requests. A single target group also offers no mechanism to detect a bad target, so this configuration does not meet the requirement of uninterrupted service when an instance stops responding.
- ✗
An Elastic IP address associated with each EC2 instance in the Auto Scaling group.
Why it's wrong here
Elastic IP addresses provide stable public addresses but do not perform health checking or failover. They also do not scale well because the account has a limited number of addresses, and associating them with instances that are replaced by the Auto Scaling group adds operational overhead without improving availability.
- ✗
An Auto Scaling group with a scheduled scaling policy that adds instances every morning.
Why it's wrong here
Scheduled scaling adjusts capacity at predictable times and does not react to a failing instance. If one instance becomes unresponsive mid-day, the schedule does nothing to remove it from service or replace it, so requests continue to fail until an operator intervenes, which the team wants to avoid.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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